I have look in the Catechism.
The Biblical quote you refered about, JR1,5 is mentionned in 2270 chapter. With Ps 139,15 too, that means that God know us physically even in the womb.
The chapter is about Abortion and prenatal diagnostic. I think you know what is write in it.
It doesn’t give us an explanation of the Bible quote. So the question on God formed us physically is still open. But he knows us, soul and body, and formed us.